As a result of changed market economy conditions on the open electricity markets and the improved technologies in the field of power electronics, the topic of variable-speed drives for energy production has gained in importance. For this purpose, double-fed asynchronous machines are preferably used, in particular at powers of above 60 MVA.
The stator of this type of machine is no different from the salient pole synchronous machines which are conventional for this application. Machines of this type are characterized by the fact that they are equipped with a three-phase winding both on the stator and on the rotor. Generally, the end windings of the rotor winding are in this case arranged on a cylindrical surface (DE-A1-195 13 457).
A corresponding (three-phase) winding scheme, for example for a rotor, is reproduced in FIG. 1, with the rotor circumference being illustrated in unrolled form in the plane of the drawing: the rotor 10 has a rotor core 11, in which axially extending winding slots 12 are provided. The winding slots 12 accommodate the winding 13, which is formed from winding bars 17, 18. Each phase is illustrated by a different type of line (short dashes, long dashes, continuous line). In each case two winding bars 17, 18 are accommodated one on top of the other in a winding slot. At the end sides of the rotor 10, the winding bars 17, 18 emerge from the winding slots 12, and the majority of said winding bars are electrically connected to one another in pairs at the ends in accordance with a predetermined scheme within an end winding 13a and 13b (connections 16). The remaining winding bars are passed to the outside as terminals 14, 15.
For the pairwise connection, in the prior art in each case one upper winding bar 18 of a first winding slot and one lower winding bar 17 of a second winding slot are bent towards one another at the end of the rotor core 11 in such a way that the two ends lie one on top of the other in the radial direction, as is reproduced in FIG. 2 in an enlarged detail for an end winding 13a′. The bar ends 19, 20 are aligned parallel to one another and one on top of the other by virtue of a second bend at the ends of the winding bars 17, 18, which are bent towards one another. The exposed (stripped of insulation) conductors of the winding bars 17, 18 form, in this region, lugs 21, 22 with a rectangular cross section, to which in each case one angular connecting part 23 or 24 is then fitted. The electrically conductive connection 16 (FIG. 1) is finally brought about by virtue of the two connecting parts 23, 24 being connected to one another.
The known formation of the end winding 13a′ shown in FIG. 2 has various disadvantages: firstly, a second bend at the bar ends 19, 20 is necessary, and this involves additional complexity. Secondly, additional copper material for the parallel bar ends 19, 20 is required, as a result of which not only are the material costs increased, but also the axial length of the end winding and the winding resistance are increased.
It has therefore already been proposed in U.S. Pat. No. 5,789,840 to do away with the second bend in the end winding in the case of a stator winding and to connect the mutually crossing ends of the winding bars to be connected by means of a special multi-part connecting part. One disadvantage with this solution, however, is the multi-part design of the connecting part, which comprises two U-shaped connecting elements (62, 64) and a rotating pin (66) arranged in the center. As a result of the multi-part design, the connecting element can be matched to different crossing angles, but is complex in terms of manufacture and installation if a large number of connections need to be produced.